Process for the dehydration of lower fatty acids with ketones and ethers



Aug. 29, 1939. D. F. OTHMER 2,170,834

PROCESS FOR THE DEHYDRA'I'ION OF LOWER FATTY ACIDS WITH KETONES ANDETHERS Filed July 3, 1936 2 Sheets-Sheet 1 KETONE LAYER GRAMS ACETICACID PER CCSOLVENT WATER LAYER 2a FIG.2. l- 526 51124 Z2 4-] l 2 $7 I 1Q g. r/ 346 f ,Rf q 3,. z rn w DISTRIBUTION I ACETIC ACI BET EN 55.WATER AND ETHE .4 I. .42 .68 .7? .60 502 T f T F U INV OR.

mem 5&5? :51,

BY W

PER CC. WA V v ATroaEYs Aug. 29, 1939. D. F. OTHMER 2,170,334

PROCESS FOR THE DEHYDRATION OF LOWER FATTY ACIDS WITH KETONES AND ETHERSFiled July 3, 1956 2 Sheets-Sheet 2 FIG. 3.

CONDE DECANTER D/LUTE ACID IN VAPOR LIQUID DEHYDRATED ACID our ACETIC'ACID WATER" ENTRAINER (KETONE, ETHER, ETC.)

" DOnaZdFOIhmeP INVENTOR Patented Aug. 29, 1939 UNITED STATES PATENTOFFICE PROCESS FOR. THE

DEHYDRATION'OF LOW- ER. FATTY ACIDS WITH KETONES AND ETHERS poration ofVirginia.

Application July 3, 1936, Serial No. 88,823

13 Claims.

for extracting acetic acid from its aqueous solutions by counter-currentliquid contact. The acetic acid after extraction may be more readilyrecovered from the solvent thanfrom the water originally present. Stillother methods have concerned themselves with the distillation. of theaqueous solution in the presence of an auxiliary liquid, which by reasonof its insolubility in water and the vapor pressure relations dependentthereupon, brings over the water in a low boiling vaporous mixture. Insuch methods (see for example, Othmer, U. S. Patent No. 1,917,391), it

is usual practice to condense the vaporous mixture of water andwithdrawing agent, separate the two layers of water and water insolublethird liquid respectively, discharge the water layer to waste (or to anauxiliary still for removing the trace of third liquid dissolvedtherein) and return the third liquid or withdrawing agent to the head ofthe column as reflux wash for the purpose of bringing over more water ina continuous operation.

I have found that certain materials of a somewhat difierent boilingrange than those ordinarily. used and exemplified by various ketones andethers are satisfactory materials to be used in the extraction process;in the azeotropic distillation process when the operation is changed aswill be noted hereinafter; or in the combined operation wherein, aftersystematic extraction of the aqueous acetic, the water dissolved withthe acetic in the solvent layer is ejected in a socalled azeotropicdistillation with the solvent itself.

The use of low boiling materials such as ethylone dichloride and ethylacetate is old in the art of removing water from acetic acid by theseseveral practices, but these low boiling materials require anexcessively large distillation column and considerable more heat becauseof the very high ratio of withdrawing agent to water in the azeotropicmixture.

One of the difliculties which has prevented the use of various materialsfor azeotropic withdrawing agents is their "tendency to come out of thesystem with the acetic acid because their boiling points are so close tothat of acetic acid that they cannot be satisfactorily separatedtherefrom by distillation and rectification.

I have found, however, that this tendency for the acetic acid to comeout of the system contaminated by withdrawing agent may be readilyovercome by the correct operation of the process as hereinafterexplained in a continuous manner and in an efficient column of the usualtype fitted with still pot or heating section, condenser and decanter asis usual practice in the use of azeotropic withdrawing materials. Thetype and arrangement of equipment is described in. Othmer, United StatesPatent No. 1,917,391; but the method of operation is substantiallydifferent, as will be indicated.

This invention has for an object to provide a process, includingazeotropic distillation with oxygenated agents, wherein the azeotropiccomposition is formed and maintained separate from concentratedaliphatic acid. Another object is to provide a process for operating adistillation unit employing oxygenated withdrawing agents wherein thelower part of the unit is operated in accordance with the simpleprinciples of ordinary rectification.

Still another objectis to provide a process for dehydrating aliphaticacids employing oxygenated withdrawing agents. It is also an object toprovide a process for concentrating the lower fatty acids which iscontinuous. Another object is to provide a process in which the sameagent may be used both as an extracting agent and as a water entrainingagent.

A further object is to provide a distillation process employingoxygenated agents for remov- 'ing water from dilute solutions of acetic,propionic and butyric and other lower fatty acids or mixtures thereof. Afurther object is to provide an extraction and distillation processwhichis applicable to lower aqueous fatty acid solutions of variousconcentrations. Another object is to provide a process employingoxygenated agents in which the water removed from aliphatic acidscarries with it to waste only a very small amount of acid.

The efficient and almost complete separation of water and acid withoutthe discharge of withdrawing agent, such as ketones or ethers, in theacetic acid may be accomplished, by the control of the amount of thewithdrawing agent in the system so that it is only in the upper part ofthe column; and considerable water is present in the acid below thelowest point where the withdrawing agent reaches. Heretofore, it hasbeen thought necessary either to have an excess of withdrawing agent inthe column so that it will exist in the column below that point Wherethe last of the water has disappeared; or, at the east, the right amountso that in working down the column, the last of the water and the lastof the withdrawing agent will be vaporized togcther and hence removedfrom the acetic acid. I have found that, by removing a part of thequantity of withdrawing agent (ketone or ether), the acid may bedischarged free of the withdrawing agent.

By such operation it will be seen that liquid passing down the columnwill flow out of the section-in which there is azeotropic withdrawingagent, still containing more or less water. Heretofore, such operationof the distilling column has been considered fatal to the removal of thelast of the water to give the anhydrous acid which is desired at thebase. I have discovered, however, that it is possible to obtainsubstantially dry acid at the base even though considerable water flowsdown with the acid out of that section which is charged with theazeotropic withdrawing agent. I explain this ability to accomplish thedehydration in a column, which according to previous practice would beregarded as insufficiently charged with withdrawing agent, on the groundthat the fraction of water present is removed from the acid in the lowerpart of the column by the ordinary rectification process; and thiswater, containing considerable acid, is passed up into the azeotropicdistillation range in which the water is separated from substantiallyall of the accompanying acid. In the usual case, it is not desirable tohave more than ten to twenty percent of water in the acid passing out ofthat part of the column which has present the withdrawing agent; andthis maximum amount of water which can besatisfactorily separated bystraight rectification in the lower part of the column wtihout the aidof withdrawing agent depends on the water present in the dilute acid fedto the column, and also on the latent heat and azeotropic ratio of thewithdrawing agent used.

If less than 25% water is present in acetic acid,- it may be separatedfrom most of the acid without the expenditure of an excessive amount ofheat-supplied in the still pot and removed in the dephlegmatorcondenser-by ordinaryrectification. The Water so removed will containconsiderable acid; in the usual case, about an equal amount. The heatrequirements are excessive, however, when dilute acids are submitted toordinary rectification, and especially is this the case when it isdesired to remove all of the water substantially free of acid.

I have discovered now, that by using the lower part of a distillationcolumn in continuous operation for ordinary rectification of the lastwater from the acetic acid, the vapors, containing all of the water andconsiderable acid, may be passed into the upper part of the columnwherein the water is completely separated in an azeotropic distillation;and the acid is allowed to fiow back into that part of the columnwherein ordinary rectification is proceeding. The liquid flowing fromthe upper part of the column to the lower, commonly called reflux washis used in this rectification just as that returned from a dephlegmatorwould be if this rectification was proceeding in a separate column.Actually, the loW- er part is factionating from the anhydrous aceticacid which is discharged in the usual way from the column base, eightyor ninety per cent acid (for example) which is passed as vapors acrossthe hypothetical division into that part of the column where thewithdrawing agent per sists and removes the water from the acid insubstantially the usual azeotropic distillation.

There is used in the lower part of the column to remove the final amountof water from acid by straight rectification the same vaporous heat asis used in the upper part of the column to complete the separation bydistillation with the withdrawing agent. That is, in my distillationcolumn the bubble platesare covered with liquid.

In the upper part of the column the liquid will includewithdrawing'agent. The vapors from the lower system contact by bubblingthrough liquid and in doing so new vapors are formed which in turncontact the liquid on the plate above. It is therefore apparent in myprocess that the vapors from the straight rectification may supply heatto accomplish the azeotropic distillation.

My process is the exact reversal of the former method of azeotropicdistillation using comparatively low boiling materials such as ethylenedichloride isee U. S. Patent No. 1,917,391) wherein the upper part ofthe column" accomplishes the azeotropic distillation and the lower partof the column is used for a straight rectification of an excess ofwithdrawing agent rather than an excess of Water as in the presentinvention.

In the use of these lower boiling withdrawing agents I have found thatit is also advantageous to work with insufiicient azeotropic liquid inthe lower part of the column.

I have found that the use of the lower part of the column for straightrectification of water from acetic acid in a two component systemenables the use of various ketones and ethers as withdrawing agentswhich boil closely to the boiling point of acetic acid, or indeed at thesame temperature or above. be more diflicult to separate from aceticacid by straight rectification than the water itself, and in the olderprocesses were considered quite impossible of utilization. It is fromthese liquids that the most efficient azeotropic withdrawing liquids maybe chosen; and I have found that much smaller amounts of liquids havingthese comparatively high boiling points are required to bring over aunit amount of water than will be required of those having lower boilingpoints. This means that the column will have less vapors to handle andhence a smaller column can be used; and since less vaporous heat isrequired, a corresponding reduction in the amount of steam used willalso be possible.

By the proper operation of this continuous process. I ha e found thatthe number of liquids which may be used for azeotropic withdrawingagents has been greatly extended. In general, the use of less than therequired amount extends the boiling range of suitable azeotropic liquidsfrom 102 (1., which was formerly regarded as the unpcr limit forcontinuous operation to about C. Many liquids in this boiling range havebeen found satisfactory and those listed below are to be regarded merelyas examples of thosz which may be used when the lower part of the columnis allowed to separate the aliphatic acid from the last of the water bystraight rectification and the upper part substantially separates thewater from the aliphatic acid by the azeotropic distillation.

Among some of the agents which may be used Such liquids may even.

are the following, with their normal boiling points-dichloromethylether106; allyl iso amyl acid based on the use of methyl propyl ketoneas an azeotropic withdrawing agent employed in accordance with theprocedure set forth herein. This ketone may contain, in the nature of animpurity, approximately 10% or less diethyl ketone. Either of these twoketones or their mixture may be used with the same results.

These ketones, individually, have maximum constant boiling mixtureswithformic acid at,

105 C. containing respectively 48 mol% di-ethyl ketone and 47 mol%methyl-propyl ketone. The well known constant boiling mixture of waterwith formic acid has a boiling point-of 107 C. and contains 43 mol% ofwater.

It would seem at first thought that either of these ketones would bevery unsatisfactory for use due to the fact that they would be as hardto separate from formic acid as the water itself.

This is, of course, the case, unless theketones are properly employed.

It would be seen, however, that anoutstanding advantage at the startover such prior art materials as pro-pyl formate, would be that theketones would increase the relative boiling point of formic acid-ordecrease its vapor pressure and thus make it somewhat easier to separatefrom water.

It has been found possible to remove the water from formic acid by theuse of these ketones at set forth in Othmer Patent No. 2,028,800 or in,

accordance with the procedure described in the present application.

In accordance with the procedure in the present application the lowerpart of the column will be used as a rectifying column to separate thewater and formic acid, producinghighly concentrated or anhydrous acid atthe base. .In this later case. it will be seen that it is necessary tothan 43 mol% at that point where the lastof the withdrawing agent leavesin order that the rectifying may proceed along with part of the vaporcomposition curve between the constant boiling mixture and anhydrousformic acid.

Because of the closeness of the vapor composition curve to the 45diagonal-i.e., the little difference between composition of vapor andliquid, or the difficulty in rectification--this dependence on the lowerpart ofthe column for straight rectification requires a very efllcientdistilling unit. It is therefore preferred to operate according to theprinciple of Othmer 2,028,800 to carry off the Water: and while this isa somewhat difficult condition to keep balanced, it issimpler than theoperation of prior art methods for formic dehydration.

For convenience of consideration in Table 1 below there is a list ofeight ketones which fall within the boiling range 102 C.-150 C. andwhich are commercially available. This by no means exhausts the list ofketones which are known and which boil within this range and which wouldbe useful for this purpose but these materials are examples and all arecommercially available at the present time. The data in this listincludes the molecular weight, the specific gravity at the boiling pointat atmospheric pressure, the solubility in water-end water in, thelatent heat in calories per gram, the azeotropic boiling point withwater, and the azeotropic ratio of solvent to water by volume. This lastpoint is found by carefully obtaining thy azeotropic ,vaporous mixture.condensing thesl vapors, and measuring the solvent and water layers.Finally there is listed the maximum strength of acetic acid which may bebest extracted by these solvents, or in other words, the strength ofacid in contact with the solvent just below the point at which perfectmiscibility is obtained. This data is believed accurate within areasonable range allowed for experimental error.

Because of the considerable insolubility of these materials in water,these materials will give a much sharper separation in the decanter,

x will carry back less water to the distilling column .forre-evaporation and will carry less solvent to the stripping column andtherefore decrease the load and steam consumption of the stripper than*is the case with certain prior art esters.

Because of the very satisfactory distribution ratios of these materialsas illustrated in the attached drawing, Fig. 1 the efficiency of therectifying column is very considerable as has been explained before; andfor a given desired sweet Water concentration, the column may becomparatively short.

Table 1 Solubilitv by weight Maximum i A Azeo 111K- Mnle- SpecificLatent Area boilw tune by Ketone cular gravity at 332 a; 1 ing pointvolume weight '20 f. j with water be ketone In water Water in Lmctedwater ill-ethyl. Methyl pro; iyl l i i v llexonc (methyl isnbutyl)Higher ketones 4:01 65 70% li-isonropyl. 35-30% ethyl isopropyL IMethyln butyl 80 to l Mesityl oxide 34% 46 to l Dipropyl i r r Methyl n amyl45% 1 4 to l While the above description has been directed to theconsideration of the group of oxygenated compounds, the aliphaticketones; I have also found and as already described that there areanumber of ethere, which are satisfactory for use in my novel process.There is following detailed information concerning some of the etherswhich are more orless commercially available together with theirphysical properties. Other ether-s would be those boiling within theboiling range of approximately 102 C.-to 150 Such ethers as thosenot'speciflcally mentioned may .be readily determined by a considerationof the permutations and combination of alcohols togive ethers in thisboiling range.

, Dibutyl' Ethyl hexyl Ether other other Molecular. weight 130 130.Specific gravity 20/20. 0. 7713 0. 8327. Boiling poiut. 142.6 143-144.Solubility in water percent by wt. 0. 04 Insoluble .l. Solubility ofwater in percent by wt 0.05 Insoluble .l. Azootropic boiling point withwager 02.9 92. 9. Azcotropic mixture by voluinei g: 2' 6 2, 45, Max.strength acetic which is best ex 70 70 or above.

trocted, percent. ,1

The ethers, such as di-butyl and the like are particularly suitable foracetic and higher aliphatic acids. However, there are a number of etherswhich may be employed in accordance with my novel procedure fordehydrating formic Iso propyl 675 C. Methyl-n butyl '70.0 C. Ethyl-npropyl 61.4 C. Ethyl t butyl73.1 C. Ethyl isobutyl 81.1 C. Ethylisobutyl 80 C. Propyl isopropyl 80 C. Methyl t butyl 552 C. Ethyl secbutyl 81.2 C.

The ethers containing an alcohol not of the straight chain configurationare advantageous for two reasons: (1) They may be readily producedcompared with the tedious and expensive method for making mixed etherscontaining two normal alcohol groups, (2) in decomposing they giverespecti've alcohols rather than explosive peroxides.

In further reference to the use of ethers for dehydrating formic acid,special mention is made of isopropyl ether.

Because of the fact that formic acid has a maximum boiling azeotropicmixture with water itself, it is even more difficult to separate fromwater than is the more familiar acetic acid. The choice of azeotropicwithdrawing agents has consequently been more limited. In previouspatents, (U. S. 1,826,302 and 1,930,146) the use of. propyl formate wascovered as being suitable I 'still pot.

for this operation and also for liquid-liquid ex- .tration of theaqueous formic acid.

It is generally desirable to use a withdrawing agent for dehydratingformic solutions having a lower boiling point than would be usuallyregarded as desirable with'acetic acid. This lower boiling point means alower boiling azeotropic mixture which in turn means a larger amount ofwithdrawing agent in the azeotropic mixture and hence a larger amount ofreflux to the column. This large amount of reflux helps to accomplishthe separation, and turns out a very small amount of formic acid at thetop of the .column in the water while maintaining a concentrated acid atthe base.

An azeotropic withdrawing agent of higher .boiling point would give asmaller amount of reflux; but because of the difficulty of separatingthe water from the formic acid, would bring over considerable acid inthe water discharge from the decanter.

In my search for suitable materials, it. was .found that isopropylether, having a normal boilingtpoint of approximately 69 C., issatisfactory .for this separation because it requires approximately 31parts of ether by weight to bring over one part of water by weight. Thusthere is a very large amount of reflux available to accomplish theseparation of water from formic acid in the column. The azeotropicboiling point is approximately 2.6 lbs. of steam per lb. of waterremoved, in addition to the heat of vaporation of the water itself (i.e. the total heat requiredexcept radiation and other losses per lb. ofwater removed is approximately that of 3.6 lbs. .of steam.

The following is an example of a run carried out employing isopropylether for dehydrating formic acid and my process wherein the lower partof the column was operated in straight rectification.

90% formic acid was diluted with water (5 to 4) to give approximately50% formic acid. This was fed into a fifteen foot column, packed withglass beads, at a height of ten feet above the Iso-propyl ether was usedas the azeotropic withdrawing material. Water was discharged with notaste of formic acid but a taste of the isopropyl ether. About 0.3% acidby titration in water layer. The process continued unchanged until theacid in the still pot-originally 50% approx-came up to the azeotropicpoint. The boiling point in the still pot had then reached 1065 where itstayed constant. Still not acid titrated about 72% acid, waterpractically ceased coming off the top, isopropyl ether circulatedaround. This isopropyl at the top titrated less than 0.1% acid.Temperature 64 to 66.

For further consideration of my invention, reference may be had to theattached drawings.

Fig. 1 is a graphic representation showing the distribution of aceticacid between water and the ketones of the present invention.

Fig. 2 is a similar representation concerning some of the ethers of thepresent invention.

Fig. 3 is a diagrammatic side elevation View of one form of appropriateapparatus which may be used in carrying out my process.

It isxtherefore, apparent from the above description that my process mayemploy a variety of different agents including both ketones and ethers.For convenience of reference I may hereinafter term these ketone andether aliphaticwithdrawing agents or entrainers as oxygenated.

Since the legends appearing on the drawings terials which are suitablefor the azeotropic' render the figures self explanatory, furtherdescription is unnecessary.

Certain of the liquids are more efficient from the standpoint of heatcosts, others may be more efficient from the standpoint of ease ofseparation of substantially pure water at the still head. In some case,as, for example, with butyl ether, I have discovered that some acid maybe found in the water at the still head unless one of the longer columnsare used. This is not always undesirable, but when acid entirely freewater is wanted, choice may be made of another material.

It will be apparent to those skilled in the art that the calculation ofthe number of bubble cap plates-if the usual plate column isused-necessary for the lower part of the column can readily be made bysetting up the customary heat balances. The maximum amount of refluxwash entering the top of this section may also be obtained by the samecalculation. With a known number of plates, and theamount of reflux washwhich is available thus calculated, it is simple to determineby theusual methods of design for a column the maximum amount of water whichmay be allowed in the acid descending from the azeotropic section ifglacial acid is to be obtained at the column base. The upper part of thecolumn in which the azeotropic distillation'is conducted may be acontinuation of the lower section with no mechanical transition ordifferences; and it is made of a suitable height to give the requiredfreedom of acid in the water discharged. If this is exceeded inpractice, it is merely necessary "to charge a small additional amount ofwithdrawing agent so that it will work down and thus lengthen thesectionin which the azeotropic distillation is being conducted. Askilled operator will immediately recognize a change of conditions inpractice by observation of changes'in the temperatures of thermometersinserted along the side of the column, and will readily apply the propercorrections.

I have found that with a bubble plate column of standard design, thatfrom about thirty to fifty plates are required, depending to some extentupon the strength of the acid to be concentrated; but to a greaterextent on the boiling point and some other physical properties "of thewithdrawing agent used.

In many cases, the same ketones'and ethers which I have found to besuitable for azeotroplc,

withdrawingagents by the use of the process described, may be used asextracting agents for the separation of the acetic acid or otheraliphatic acid from the bulk of the water before distillation. While theuse of extracting solvents having relatively high boiling points isknown (U. 8. Patent 1,839,932,) it has hitherto been necessary to addstill another liquid to perform the azeotropic withdrawal of the waterwhich necessarily accompanies the acetic acid.

By the use of my method of azeotropic distillation above described, itis possible to accomplish the extraction first and then' the azeotropicdistillation with the same material. While all madistillation are notusefulfor a preliminary extraction step, the ketones and ethers which Ihave described are satisfactory for both operations. I have also foundthat this process of azeotropic disti11ation-whereby insufficientWithdrawing agent is present in the distillation system to form theazeotropic mixture with the water present closure as limited and definedby the appended claims.

In particular, it may be noted that any standard type of extractorvand/or distilling column or columns which are efficient for this purposemay be used; that a single column may be used for both the azeotropicdistillation and the straight rectification of water from acid or acids,or that two columns may be used with or without a still pot and heatingunit in between. The dilute acid may be fed into the distilling columnor columns either in a liquid or vaporous state; and the discharged acidmay be either partly or completely dehydrated and passed from thedistillation system in either a liquid or vaporous condition. Aso, afterthe azeotropic distillation, the condensate from the condenser may beseparated into layers comprising substantially pure water andsubstantially pure withdrawing agent respectively, and the formerdischarged to waste or to an auxiliary still for.recovering the trace ofwithdrawing agent dissolved therein, while the latter is returned to thehead of the still as reflux wash, or divided into two or more streams.one of which. enters the top of the distilling column and the rest ofwhich enters the column at a lower point or points. Likewise, itisapparent that in some cases other chemical materials'than thewithdrawing liquid itself may be added in such a way that thewithdrawing liquid will be manufactured in the column. Also as alreadydescribed various mixtures of withdrawingliquids may be used incombination.

Having described my invention, what I claim and desire to secure byLetters Patent is, as follows:-

aqueous solutions of the lower fatty acidsby distillation in thepresence of withdrawing agents y from the group'gbgnsisting of ketonesand ethers for the uyai' ;.oi; water, the separation of thelast'partioftheimater from the lower aliphatic .acid by straight"rectification, said rectification using the same vaporous heat which isthereafter passed to the 'azeotropic distillation and keeping saidwithdrawing agent out of the resultant dehydrated fatty acid at alltimes that it occurs dehydrated acid.

2. The process for group consisting of ketones and ethers whichseparating water from lower fatty acid or acids by distillation with an'aliphatic oxygenated withdrawing agent from the forms an azeotropicmixture in the still head,

the vaporous mixture is condensed, the con 'densate separated into awater and a withdraw- V ing liquid layer, the water layer discharged andthe oxygenated withdrawing liquid layer returnedto the still head toremove more water, the partially concentrated lower fatty acid or acidspassed out of the upper part of the distilling column containingwithdrawing liquid to a. lower part which contains no withdrawingliquid, additional water separated by straight rectification of thelower fatty acid or acids in the lower part of the column, the highlyconcentrated or anhydrous lower fatty acid or acids removed from thecolumn base, keeping said withdrawing agent out of said concentratedfatty acid at all times that it occurs as concentrated acid, and avaporous mixture, containing most or substantially all of the water,passed upwardly from said lower part of the distilling column to saidupper part.

3. In the process of dehydrating aqueous solutions of the lower fattyacids by extraction and distillation in the presence of oxygenatedaliphatic withdrawing agents from the group consisting of ketones andethers having a normal boiling point between 102 and 150 C. for theremoval of water, the use of insufficient withdrawing agent to form anazeotropic mixture with water n the lower part of the distilling columnand keeping said oxygenated aliphatic withdrawing agent out of thedehydrated acid at all times.

' 4. In the continuous process of dehydrating aqueous solutions of thelower fatty acids by distillation in the presence of a ketonewithdrawing agent, the separation of the last part of the water from theacid or acids by straight rectification and keeping the ketone out ofthe dehydrated acid at all times that it occurs as dehydrated acid 5. Inthe continuous process of dehydrating aqueous solutions of the lowerfatty acids by distillation in the presence of an ether withdrawingagent, the separation of the last part of the water from the acid oracids by straight rectification and keeping the ether out of thedehydrated acid at all times that it occurs as dehydrated acid.

6. In the continuous process of dehydrating aqueous solutions of thelower fatty acids by distillation in the presence of oxygenatedaliphatic withdrawing agents from the group consisting of ketones andethers, the separation of the last part of the water from thefatty acidsby straight rectification, said rectification using the same vaporousheat which is thereafter passed to the azeotropic distillation andkeeping the oxygenated Withdrawing agents out of the dchydrated acids atall times that they occur as dehydrated acids.

'7. In the continuous process of dehydrating aqueous solutions of thelower fatty acids by distillation in the presence of ketone withdrawingagents from the group consisting of ethyl propy ketone, methyl butylketone, allyl acetone, dipropyl ketone, diethyl ketone, methyl propylketone, methyl isobutyl ketone, methyl normal butyl ketone, methylnormal amyl ketone for the removal of water, the separation of the lastpart of the water from the acetic acid by straight rectification, saidrectification using the same vaporous heat which is thereafter passed tothe azeotropic distillation and keeping the ketone withdrawing agentsout of the dehydrated fatty acids at all times that they occur asdehydrated acids.

8. In the process of dehydrating aqueous solutions of the lower fattyacids by distillation in the presence of ethers boiling within the range50-150 C. and capable of the removal of water as an azeotrope, the useof insufiicient ether to form an azeotropic mixture with water in thelower part of the distilling column and keeping the ethers out of thedehydrated fatty acids at all times that they occur as dehydrated acids.

9. In the continuous process for dehydrating aqueous solutions of formicacids including azeotropic distillation in the presence of isopropylether for the removal of water, the separation of the last part of thewater from the formic acid by straight rectification, said straightrectification supplying at least a part of the same vaporous heat whichis thereafter passed to the azeotropic distillation and keeping theisopropyl ether out of the dehydrated formic acid at all times that itoccurs as dehydrated acid.

10. In a process for dehydrating aqueous solutions containing at leastone of the lower fatty acids by distillation in the presence of ethylhexyl ether as a withdrawing agent for the removal of water, theseparation of the last part of the water from the acid or acids bystraight rectification and keeping the ethyl hexyl ether out of thedehydrated acid at all times that it occurs as de-' hydrated acid.

11. In a process for dehydrating aqueous solutions containing at leastone of the lower fatty acids by distillation in the presence of normalbutyl ether for the removal of water by azeotropic distillation in theupper part of the distilling unit, the use of insufficient normal butylether to form an azeotropic mixture with the water in the lower part ofthe distilling unit andkeeping the butyl ether out of the dehydratedacid at all times that it occurs as dehydrated acid.

12. The process for separating water from aqueous formic acid solutions,which comprises distilling the aqueous formic acid solutions in adistilling column having a still pot,with ketones which form anazeotropic mixture with the water, condensing the azeotropic mixture,permitting the condensate to separate into a water layer and a ketonelayer, discharging the water layer and returning the ketone layer todistillation for re moving more water, employing insufficient ketoneagent to form an azeotropic mixture with the water in the lower part ofthe distilling column and separating the last part of the water from theformic acid by straight rectification so as to give dehydrated formicacid in the still pot and keeping the ketone out of the dehydratedformic acid at all times that it occurs as dehydrated acid.

13. In the continuous process of dehydrating aqueous solutions of thelower fatty acids by distillation in the presence of ketone withdrawingagents from the group consisting of ethyl propyl ketone, methyl butylketone, allyl acetone, di-' propyl ketone, diethyl ketone, methyl propylketone, methyl isobutyl ketone, methyl normal butyl ketone, methylnormal amyl ketone for the removal of water, the use of insufficientketone withdrawing agent to form an azeotropic mixture with water in thelower part of the column and the separation of the last part of thewater from the acid or acids by straight rectification and keeping theaforementioned agents out of dehydrated acid at all times that it occursas dehydrated acid.

' DONALD F. OTHMER.

